MySQL:
1&1 supports both MySQL 4 and 5, and SS had no problems recognising the database once I'd input the correct details into the installation page.

PHP:
By default 1&1 serves PHP pages as PHP4. To get PHP pages served as PHP5 you need to add the following line to your .htaccess file:

AddType x-mapp-php5 .php

mod_rewrite:
After SS has run the installation script, it may give a warning that mod_rewrite is not working correctly. To fix this add the following line to your .htaccess file within the ### SILVERSTRIPE START ### block of code:

RewriteBase /

Finally, SS may complain that is does not have write permissions for your .htaccess file. We had this problem and could not figure out why SS was complaining when the file had permissions of 644.

We realised that the problem was related to the HTTP password protection that we had put on our 'test' installation directory.

To add HTTP password protection to the directory, we had to use 1&1's admin 'control panel' as it modifies an htpasswd file that we do not have permission to access, and also creates a new .htaccess file.

This meant that 1&1's superuser was the owner of the .htaccess file, not us.

The way we fixed this was to download the .htaccess file created by 1&1 by FTP to a local directory, delete the original .htaccess file and then upload it again from the local directory to the server. The .htaccess file was exactly the same, it's just that the 'owner' was now us, not 1&1.

This meant that SS was happy again and could modify the .htaccess file to its heart's content. Yaay!

Thanks and I did almost the same thing and I'm on 1&1 USA and having problems. I guess it's hit or miss. I didn't seem to have a password issue or the other issue you had but the CMS is not loading and I get a null object error in IE when loading the page.